Therapeutic and diagnostic benefits are being attributed to the stimulation of various tissues by electric currents in spite of the fact that little is known with respect to the pathways taken by these currents and consequently the site, or sites, of action. It is, however, known that tissue is neither homogeneous ob isotropic and that these characteristics may change by a factor of ten within a few millimeters. It is intuitively obvious, for the well being of the patient, that the minimum amount of current and/or power injected into the living system to perform a specific function is desirable. Knowledge of current pathways for specific electrode locations will furnish information as to probable sites of action allowing for a better analysis of the mode of action and it will also allow electrodes to be so placed as to minimize the amount of current required for each specific task. Previous work by the principal investigator (PI) has demonstrated a system that is capable of making in vivo measurements of local current densities as well as specific impedance. This previous work required manual manipulation of placement of the sensing element as well as manual manipulation of the electronic devices used for actual measurements. As a result, the time consumed in the process contributed significantly to the errors and reduced the number of sites that could be investigated in any one animal preparation. Although the concepts were eminently satisfactory, it was not practical to collect enough information for mapping the currents resulting from any particular electrode location. The proposed research will comprise development of the previous measurement system into an automated measurement system so that literally hundreds of sites may be measured in a matter of minutes. The degree of control made possible by this automatic process will also increase the degree of accuracy by an order of magnitude. Additional research will then involve the actual gathering of data for common electrode locations and an analysis of the actual current pathways. This work will be done in vivo with cats to gather preliminary data with regard to the functioning of the new system and macaque monkeys as models of the human system.